Author(s): Francisco Taveira Pinto; Paulo Rosa Santos; Jose Victor Ramos

Linked Author(s): Francisco Taveira Pinto

Keywords: Coastal erosion; Sea level rise; Climate change

Abstract: Coastal erosion has gained importance in many countries with coastal zones exposed to severe maritime conditions. Portugal, due to its location in the North Atlantic, is no exception. At global level, the sea level rise is presently one of the main drivers of coastal erosion and therefore several interventions have been designed and build to mitigate its consequences, including hard structures and natural based solutions. However, any type of intervention implemented to stabilize the coastline and increase the resilience of the beaches can induce significant changes in the local morphodynamics because bottom velocities, currents and sediment transport itself are changed in direction and magnitude. The main purpose of this paper is to study the phenomena that can occur near detached coastal protection breakwaters, such as scour and accretion. Therefore, Carneiro beach, located near Douro river mouth, more precisely north of Felgueiras’ breakwater in Porto, has been used as a case study. This beach is often affected by severe maritime environmental conditions so that, during storms, waves are able to overtop the seawall of D. Carlos Avenue. In order to mitigate risks, Consulmar Lda designed a coastal protection intervention composed of five detached breakwaters. The experimental study of this new coastal protection solution took place at the wave tank of the Hydraulic Laboratory of the Hydraulics, Water Resources and Environment Division of the Faculty of Engineering of the University of Porto. In this study a geometric scale of 1/60 was used in order to be able to represent the area of interest and the bathymetry of the beach up to a depth of circa 13 m. The intervention consisted of three different types of structures: two vertical and three rubble mound breakwaters (two with the armor layer composed of rocks and the other one of Antifer blocks). Around 53 experimental tests were carried out, by combining four water levels, three peak wave periods and multiple significant wave height. The analysis of the results is focused in the reduction of wave energy provided by the breakwaters and on the patterns of sediment transport around the structures, in order to identify and discuss scour and accretion phenomena. The results obtained in the physical model show that in vertical breakwaters there is a higher scour phenomena on the sea side compared to the other structures due to its higher reflection coefficient. The scour phenomena also occurs where there is a contraction of the steady streaming, in this specific case, between detached breakwater 2 and 3. Finally, the results show that on the lee side the accretion phenomena occurs, with higher volume on the lee side of Felgueiras’ breakwater and also of breakwater 2 and 3.

DOI: https://doi.org/10.3850/IAHR-39WC252171192022525

Year: 2022